Electrical plug and receptacle connections, particularly those carrying relatively large amounts of electricity, can pose several dangers, including fire and death. For example, common household electrical receptacles carry alternating current at either 120 volts or 240 volts. A typical plug used with these receptacles has either two or three conductors that extend unshielded from one end of the plug's body. Due to the length of the conductors and the locations of the contacts within the receiver, there is a point where the plug is energized but the conductors are not fully inserted into the receptacle, leaving portions of the energized conductors exposed on the top, sides, and bottom of the plug.
In such a partially-inserted position, there can be enough space between the plug body and the receptacle that an object or a person's finger, particularly a finger of an infant or young child, can contact one or more of the conductors. A person touching one of the energized conductors will receive a shock, possibly resulting in death. In addition, if an object made of a conductive material, such as a metal necklace, falls in the space between the plug body and receptacle and contacts two of the conductors, the object will cause a short circuit and possibly a spark that could cause a fire. Although the foregoing dangers are generally widely known and have been known for many years, the basic design of the household receptacles and plugs has not changed.
Several attempts have been made at providing electrical plugs and receptacles that provide safety features for preventing the above-mentioned dangers. For example, U.S. Pat. No. 5,248,268 to Rinker shows a safety plug and receptacle having a plug that includes non-conductive prongs that contain the conductors. The conductors cannot be touched while the prongs are being inserted into the mating receptacle. Another example is the shielded-conductor plug and receptacle shown in U.S. Pat. No. 4,725,240 to Braverman. This type of connection is designated as an IEC 320 connection. The problem with these safety plugs and receptacles is that they are not compatible with the many millions of conventional receptacles and plugs presently in use throughout the world.
In the United States, for example, if building codes were changed to require the general use of receptacles and plugs of the type shown in the Rinker patent, there would be a great resistance to a change-over because the new receptacles would not be compatible with existing plugs and the new plugs would not be compatible with existing receptacles. A similar situation would result from a requirement to switch to using the IEC 320 type connection shown in the Braverman patent. Although IEC 320 connections are currently available, they are generally used only at the end(s) of a power cord that engage(s) a piece of equipment, such as a computer CPU housing and/or monitor.